viernes, 4 de mayo de 2012

RV: Beauty Baryon Fits Physics

Since the 1960s theoretical phsycists have been working with a veritable elementary particle zoo that underlies the more familiar nucleic parts of atoms — electrons, protons and neutrons. And slowly over decades and with the help of expensive atom smashers those theorized particles are being experimentally observed, thus moving from theory into reality.

Six Types of Quarks over Three Generations

It all started with Murray Gell-Mann, who noticed that during a Stanford linear accelerator experiment where protons collided with electrons traveling near the speed of light that three shadowy blobs appeared inside the atomic nucleii. He called these new fundamental building blocks of atoms quarks. Protons and neutrons are the subatomic particles also known as baryons.

In particle physics, the baryon family refers to particles that are made up of three quarks. Quarks form a group of six particles that differ in their masses and charges. The two lightest quarks, the so-called “up” and “down” quarks, form the two commonly known atomic components, protons and neutrons. Scientists have found all the baryons that are composed of the three lightest quarks — up, down and strange — quarks. But only very few baryons with heavy quarks have been observed in the lab. They can only be generated artificially in particle accelerators and are highly unstable.

Now several years after the Large Hadron Collider below the Franco-Swiss border began recreating the moments following the Big Bang in the Universe particle physicists have put another theoretical particle puzzle to rest.

Cornell University physicist James Alexander says the discovery of the new Xi_b* (pronounced ky-bee-star) particle is “another brick in the wall.”

The Xi_b* particle belongs to the so-called beauty baryons, particles that all contain a heavy bottom quark, also known as a beauty quark.

Researchers from University of Zurich’s Physics Institute detected a baryon with one light and two heavy quarks. Xi_b* has one up, one strange and one bottom quark. With this observation by physicists Claude Amsler, Vincenzo Chiochia and Ernest Aguiló two of the three baryons theorized to have that usb composition have been experimentally observed.

The Compact Muon Solenoid (CMS) detector found evidence of the new particle’s rapid decay but didn’t see it directly because it is such a short-lived subatomic particle, existing for just a fraction of a second before decaying into 21 equally fleeting particles.

Following the discovery CMS physicist Vincenzo Chiochia, a co-discoverer of the new particle, told Symmetry Breaking magazine, “Finding this particle is really very hard.”

Chiochia says, “Finding this complicated decay in such a messy event makes us confident in our abilities to find other new particles in the future.”

CMS scientists believe they have confirmed Xi_b*’s existence to a sigma level of five, which means the researchers are 99.99 percent confident that the result is more than a chance occurrence.

Known and Theorized Subatomic Particles Make the Particle Zoo of the Standard Model

The discovery of the new particle confirms the long-held theory of how quarks bind. It is part of quantum chromodynamics, which predicts how quarks combine to form heavy particles, but had never before been observed. It also helps to explain the strong interaction, one of the four basic forces of physics which determines the structure of all matter.

This is only the second particle discovery at CERN since the LHC began smashing atoms in 2008.